This is a noob level question.
i've got two models: Patient and Provider joined through a table Chart.
i used the association "has_many :through" rather than "has_and_belongs_to_many" because i need to have another column added to the Chart table [called patient_mrn] which i understand that i cannot do with the "has_and_belongs_to_many" scenario.
the Patient model has:
has_many :charts
has_many :providers, :through => :charts
the Provider model has:
has_many :charts
has_many :patients, :through => :charts
and the Chart model has:
belongs_to :patient
belongs_to :provider
i am trying to call a where method on the Patient model to retrieve all patients with the conditions that:
-the provider_id in the Chart join table for that patient equals a given value [#exam.provider_id] and
-the patient_mrn in the Chart join table for that patient equals a given value[#exam.patient_mrn].
this is what i came up with to try but it clearly isn't working. Where am i going astray?
#patient = Patient.where(:patient.chart[provider_id] => #exam.provider_id,
:patient.chart[patient_mrn] => #exam.patient_mrn)
Joining tables is what you need to do in order to specify conditions on a model's associated table. (Look at the section on specifying conditions for an example of what you're looking to do).
But, in short, you want to join to your chart table and specify conditions on that. Your query should probably look something like:
#patients = Patient.joins(:charts).where(:charts => { :provider_id => #exam.provider_id, :patient_mrn => #exam.patient_mrn })
This should return all Patients whose chart has the given provider_id and patient_mrn.
Related
I have four kinds of records. Teams. Coaches. Players. and Families.
Teams have a one to many association with Coaches.
Coaches have a one to one association with Players.
Players have a many to one association with Families.
What I need to find are specific families that are associated with certain Teams. However due to their separation i can't just go Team.last.family.
Is there a way to leap over the Players and Coaches and do a query from the clinics straight to the family?
Most likely you will need to make use of the joins method.
If you provide more details of your model code and schema we could provide more details, but it will be something along the lines of.
Family.joins(some_join_object).where(some_sql_search_string)
Once you have a join table that includes all the columns you want, specify the conditions you would like to filter on.
Family.joins(:players, :coaches, :teams).where("families.name='Wesley' and teams.name='Crushers'")
Here is an example from the provided link.
class Category < ApplicationRecord
has_many :articles
end
class Article < ApplicationRecord
belongs_to :category
has_many :comments
has_many :tags
end
class Comment < ApplicationRecord
belongs_to :article
has_one :guest
end
class Guest < ApplicationRecord
belongs_to :comment
end
class Tag < ApplicationRecord
belongs_to :article
end
12.1.3.2 Joining Nested Associations (Multiple Level)
Category.joins(articles: [{ comments: :guest }, :tags])
This produces:
SELECT categories.* FROM categories INNER JOIN articles ON
articles.category_id = categories.id INNER JOIN comments ON
comments.article_id = articles.id INNER JOIN guests ON
guests.comment_id = comments.id INNER JOIN tags ON tags.article_id =
articles.id
Or, in English: "return all categories that have articles, where those
articles have a comment made by a guest, and where those articles also
have a tag."
How would you set up an activerecord/datamapper association for the following scenario:
A user creates a "bookshelf" which has many books(a book object just has an isbn that is used to query an api, and has_many review objects associated with it). Let's say Jack creates a "bookshelf" with a book object. Then, lets say that Jill creates a "bookshelf" with the same book object(it has the same id and the same reviews). The book object has the following code as of now:
class Book < ActiveRecord::Base
has_many :reviews
end
Then, when you view the page for a book (you click the link to it from the "bookshelf" created by Jack) you should see the same book object when you clicked the link to it from Jill's "bookshelf" (e.g. both "bookshelves" have a link to /books/23 because they have the same book object).
I have not been able to figure this out with the has_many association because that requires me to make a new book each time a user adds a book to their "bookshelf." I have trouble understanding the has_and_belongs_to_many relationship, is that what should be used here? I was not able to find any similar questions on SO, so any help is greatly appreciated.
I am using Rails 4 with Ruby 2.1.
Here is a drawing of what I would like to accomplish:
Drawing
Yes, you would have to define many-to-many relationship between a Bookshelf and a Book. There are two ways to achieve this in Rails:
Option 1) Use has_and_belongs_to_many
See guide
According to official documentation has_and_belongs_to_many association:
Specifies a many-to-many relationship with another class. This associates two classes via an intermediate join table. Unless the join table is explicitly specified as an option, it is guessed using the lexical order of the class names. So a join between Developer and Project will give the default join table name of “developers_projects” because “D” precedes “P” alphabetically.
So, your classes should look like this:
class Bookshelf < ActiveRecord::Base
has_and_belongs_to_many :books
end
class Book < ActiveRecord::Base
has_and_belongs_to_many :bookshelves
has_many :reviews
end
Add a join table generation to your migrations:
class CreateBooksBookshelvesJoinTable < ActiveRecord::Migration
def change
create_table :books_bookshelves, id: false do |t|
t.belongs_to :book, index: true
t.belongs_to :bookshelf, index: true
end
end
end
This will create a books_bookshelves table in your database. The table will have no primary key. There would be two foreign keys to your models Book and Bookshelf.
So, if you call self.books in the context of an user's bookshelf, you will get a list of books in the bookshelf. Vice versa, calling self.bookshelves in the context of a book will return a set of bookshelves the book belongs to.
The problem with this approach is that every time you add a new book to the bookshelf a new record is created in the database. If you are okay with that, there is no easier option than using has_and_belongs_to_many association. Otherwise, I recommend you to go with the Option #2.
Option 2) Use has_many :through
Another option is to use has_many, :through association (see guide). You would have to define one more model to do that, but it might come handy in some use cases (see below for an example).
Your classes should look like this:
class Bookshelf < ActiveRecord::Base
has_many :books, through: :books_bookshelves
has_many :books_bookshelves
end
class Book < ActiveRecord::Base
has_many :bookshelves, through: :books_bookshelves
has_many :books_bookshelves
has_many :reviews
end
class BooksBookshelf < ActiveRecord::Base
belongs_to :book
belongs_to :bookshelf
end
Probably the best thing about using has_many :through association is that it allows you to add custom columns to the join table (e.g. add column count to keep track how many books of the same type are there in the bookshelf).
The migration would look pretty much the same as the one we used in Option 1, except for the fact we are adding an unique constraint on the foreign keys (please note that adding the constraint is optional):
class CreateBooksBookshelvesJoinTable < ActiveRecord::Migration
def change
create_table :books_bookshelves, id: false do |t|
t.belongs_to :book, index: true
t.belongs_to :bookshelf, index: true
# add your custom columns here
end
add_index :books_bookshelves, [:book_id, :bookshelf_id], unique: true # to make sure you won't create duplicate records
end
end
By going with this approach, adding a new would be a bit more complicated as you would have to make sure you are not inserting duplicate records in the join table. (However, you may remove the unique constraint from the migration, to achieve exactly the same kind of behavior as you would get with has_and_belongs_to_many.)
I am trying to find records that have a has_many relationship in rails using activerecord. I am having a difficult time phrasing this question but here is what I would like to find:
has_many :var, :through => :line
The above line of code is included in a model. I want to return records that have a certain :var associated with it. So if, for example, :var = 1234, I'd like to return all records that have that associated with it.
Assuming your main class is called Order, line is a belongs_to relation for Order, vars is a has_many relation for Line, and you are searching for the Var id
Order.joins(line: :vars).where('"vars"."id" = ?', 1234).uniq
Based on your comment i believe you need something like this
Order.where(:var => 1234)
or if you prefere plain sql
Order.where('var = 1234')
Activerecord has plenty of documentation on this, for example here
I have two separate has many through one relationships pointing to the same objects.
Users have many photos through photo_relationships
Users have many photos through votes
In my controller I'm trying to show all of the photos for the user through this code:
#user = User.find(params[:id])
#photos = #user.photos
However, the Inner Join is being controlled by whatever has_many relationships is mentioned last in the User model, in this case votes. Is there a way to specify what inner join is used such as:
#photos = #user.photos( joins: :photo_relationships)
Do something like this:
class User
...
has_many :voted_photos, class_name: 'Photo', through: :votes
has_many :relationship_photos, class_name: 'Photo', through: :photo_relationships
end
I have this model "Comment" which is given by a model "User" for a given "city" and "department".
While creating the schema for table "comments", I put in columns city_id, department_id and user_id which should act as foreign keys to respective ids in tables cities, departments and users.
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :city
belongs_to :department
end
Cities and Departments are independent tables which are populated with reference data (which would be used to populate in the forms.
When I try to access comment.city.name, I get a "undefined method `name' for nil:NilClass".
Table cities is defined with columns -"id", "name" and "symbol".
What is the root cause of this error?
What else do I need to do ? I have tried even by putting has_many :feedbacks in class City and class Department (even though it should not happen because they are independent of comments). I am missing something basic here, it seems.
Thanks,
Ashish
I think you need a has_many to go with every belongs_to. So each of your classes that comments belong_to (User, City, Department) should have
has_many :comments